The present invention relates to a semiconductor device and its production process, particularly to a semiconductor device having a cobalt silicide film and its production process.
With the recent trend toward higher integration and miniaturization of the semiconductor devices, reduction of contact resistance at the joint of metal wiring and silicon substrate has become essential for high-speed operation. Regarding the techniques for reducing contact resistance, for instance JP-A-08-78357 suggests to form a cobalt silicide film on the diffusion layer (source/drain) or polycrystalline silicon electrodes on a silicon substrate.
However, when the diffusion layer is made shallow and the cobalt silicide film is thinned with miniaturization of the semiconductor devices, there arises the new problem that the cobalt silicide coating, which was film-like when formed, is coagulated by a high-temperature heat treatment in, for instance, the capacitor forming step and takes a partially insular configuration, causing a rise of resistance.
The object of the present invention is to solve the above problem and provide a semiconductor device having a cobalt silicide film which is proof against coagulation and remains low in resistance even if reduced in thickness, and a process for producing such a semiconductor device.
Rise of resistance of the cobalt silicide film is attributable to the insular coagulation of the cobalt silicide which occurs when the cobalt (Co) atoms composing the cobalt silicide film are diffused mostly along the crystal grain boundaries and recombined with silicon in a heat treatment at around 800xc2x0 C. or above. Therefore, for preventing the rise of resistance due to the coagulation of cobalt silicide film, it is expedient to inhibit the diffusion of cobalt atoms in the cobalt silicide film.
On this concept, the present inventors disclosed that it is possible to inhibit the grain boundary diffusion of Co atoms in the cobalt silicide film when a specific elementxe2x80x94an element having a smaller atomic radius than Co atom and specified by the fact that the inter-hetero-atomic energy between this element and Co element is not more than 20% smaller or greater than the inter-iso-atomic energy of Co elementxe2x80x94is contained in said cobalt silicide film. That is, it was found the diffusion of Co atoms can be inhibited by containing nickel or iron element in the cobalt silicide film, and that in this case, the ratio of nickel or iron element to cobalt in said film should be preferably 0.05 to 50 atomic %, more preferably 0.05 to 18 atomic %.
It was also found that the use of multi-stage sputtering or an alloy target is suited for forming the said cobalt silicide film.